after copying the thunderbird profil from the old laptop to the new one, at one account it only showed a small part of all emails.

Unfortunately, there are many documented ways to transfer a profile, and some are problem-prone. If the transfer was done outside of thunderbird all should be there. Here are suggested steps: ''' BACKUP ''' # ensure thunderbird is not running # enter %appdata% in search window on task bar and press Enter key # this should open windows file explorer in Appdata\roaming folder # highlight the Thunderbird folder and copy to external media ''' RESTORE ''' # ensure thunderbird is installed, run once, and NOT running # enter %appdata% in search window on task bar and press Enter key # delete the thunderbird folder # you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. # start thunderbird and all should be there This process, by using windows file explorer, ensures that every component is transferred. This especially applies to POP accounts, as their files are on the PC and readily copied. If the old profile is still available, we can assist. Posting screenshot of the old profile's folder for the POP account will be a good start, plus a screenshot of the current profile's POP account folder. Let us know what guidance you need there.